Method Of Manufacturing A Crankshaft And A Half-Finished Crankshaft

Abstract

To cope with requirements for strict accuracy of crankshafts while alleviating the task of controlling a forming process, a preliminary machining step (S117) is added before primary mass balance measurement (S118) prior to boring of center holes into opposite end surfaces of a crankshaft mold. In the preliminary machining step (S117), balance weight portions of the crankshaft mold are machined.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]The present application is a continuation application of PCT / JP2007 / 063627, filed Jul. 3, 2007, which is incorporated herein by reference in its entirety.FIELD OF THE INVENTION[0002]The present invention relates to a crankshaft for use as an engine output shaft, and more particularly, to a method of manufacturing a crankshaft and a half-finished crankshaft.BACKGROUND OF THE INVENTION[0003]Crankshafts for use as engine output shafts are roughly classified to cast crankshafts and forged crankshafts depending on the forming process. Cast crankshafts are mainly used in lower rotation type engines and small engines with relatively small engine torques. Forged crankshafts are used in high rotation type engines and large engines with relatively large torques because they have compact metallographic structure and can be improved in mechanical properties by adding heat treatment after forging, if desired.[0004]Manufacturing of a crankshaft, either...

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Benefits of technology

[0012]It is therefore an object of the present invention to provide a method of manufacturing a crankshaft and a half-finished crankshaft, which includes a forming process, a machining process and a mass balance adjustment process and alleviates the task of supervising or watching the forming process while satisfying the requirement of strict product accuracy of the crankshaft.

[0019]Insertion of the preliminary machining step (S2) prior to the mass balance measurement of the treated crankshaft mold and the boring of center holes contributes to determining more adequate positions of the center holes. As a result, errors of the crankshaft mold as forged or cast (S1) impose less labor to later mass balance adjustment (S6) after the final finish machining (S5) as compared with the existing method. In addition, errors of the crankshaft mold as forged or cast (S1) impose less labor to the finish machining step (S5) as well. Therefore, the significance of seeking more production accuracy of the crankshaft mold as forged or cast by forging or casting dies is diluted. This permits manufacturers of crankshaft molds to save their efforts for maintenance of the casting or forging dies, and allows even freer designs of casting or forging dies. That is, any draft angles more desirable for facilitating formation and separation of crankshaft molds from the dies are acceptable. Furthermore, it is also possible to omit one or both of the coining step S13 and the shot blasting step S16 described in the explanation of the existing manufacturing process. Thereby, the cost required for manufacturing and preparing treated crankshaft molds, i.e. ready-to-machine crankshaft stocks, can be reduced.

[0020]In addition to the above-mentioned advantages, since the method according to the present invention enables more adequate center holes, it makes the control of finish machining (S5) easier and makes it possible to comply with strict requirements of production accuracy of crankshafts. Further, as a side advantage, since the amount to be corrected in the mass balance adjustment of the crankshaft is reduced, the number of balance adjustment cavities to be made in the balance weight portions of the crankshaft as well as the workload for mass balance adjustment can be reduced.

Problems solved by technology

In the environment with increasingly strict requirement for product accuracy of crankshafts, engineers' efforts for enhancing the product accuracy of crankshafts by strictly controlling the forming process have already reached a limit, and such control becomes more and more costly with increased strictness.

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